1. Field of the Industrial Application
The present invention relates to an improvement in a twin drum type continuous casting apparatus and a continuous casting method in which a change in shape caused by a thermal load of water-cooling drums is controlled.
2. Description of the Related Art
A conventional twin drum type continuous casting apparatus (Japanese Patent Laid-Open Application No. Hei 2-104449), which is a kind of a thin plate continuous casting apparatus, is shown in FIGS. 9 and 10.
As shown in these drawings, molten steel R is continuously fed to a casting mold portion defined by a pair of water-cooling drums 01 which are rotated in opposite directions as indicated by arrows and a pair of side dams 02, and is cooled by outer circumferential walls of the water-cooling drums 01 to thereby continuously cast a thin plate cast piece W. A water feed port 01a, a water discharge port 01e, a number of water feed passages 01b, a water cooling passage 01c along the outer periphery of each water-cooling drum 01 and a water discharge passage 01d are provided in an interior of each water-cooling drum 01. Heater blocks 03 are internally provided over an entire circumferential wall of both end portions of each water-cooling drum 01.
In this casting apparatus, when the molten steel R is fed to the casting mold portion, the outer circumferential portion of each water-cooling drum 01 is thermally expanded with both its ends being extended in a width direction of the roll. In accordance with this expansion, the water-cooling drum 01 is shrunk and deformed in the radial direction by .delta. as indicated by dotted lines in FIG. 11(a). Accordingly, an interval between the two water-cooling drums 01 is further increased by 2.delta. at both ends beyond the interval in the central portion. Also, a thickness at both end portions of the workpiece to be cast is increased by 2.delta., resulting in a worse plate shape.
Therefore, cooling water is fed from the water feed port 01a to the water cooling passage 01c, and at the same time a current is supplied to the heater blocks 03 to heat both end portions of each drum. As a result, as shown by dotted lines in FIG. 11(b), the end portions are expanded and deformed by .delta. in the radial direction to cancel the thermal deformation caused by the above-described molten steel R to equalize the interval over the entire width of each drum.
In this case, a planar shape detector (not shown) is provided at the outlet of the cast piece W to periodically detect the plate thickness over the entire width of the cast piece W. On the basis of the detection signal, the amount of heat generation of each heater block 03 is adjusted to control the thermal expansion amount at both end portions of each drum and to well control the plate shape of the cast piece W.
As described above, in the conventional continuous casting apparatus, a method is adopted in which both end portions of each drum are heated and expanded by the heater blocks 03 internally provided in both end portions of each drum to thereby perform shape control of the outer surfaces of the water-cooling drum. However, since the thermal capacitance of each drum 01 to be heated is large, a deformation responsibility of the shape of the outer surfaces of the drum to be controlled is low, and it would be difficult or impossible to timely control the workpiece to be continuously cast timely. The conventional apparatus suffers from such a problem.
Also, since the heater blocks 03 are internally provided in each drum 01, the heating with the heater blocks 03 is non-uniform, and it would be impossible to suitably control the shape of the workpiece to be continuously cast.